There are a number of key focuses for operators of telecommunications networks. These include network construction, building services onto the network, and problem-finding during both the running and the constructional stages of the network. Implementation of the last of these key focuses relies on detectors for monitoring erroneous behaviour. It is often the case, however, that during normal network operation the network is in a variety of states. Some parts may be running service, some parts may be under repair, other parts may be under construction and other parts may be modified or adjusted and so on. Detectors have a habit of generating large streams of erroneous behaviour indicators during times when the network is in a state of flux. This can lead to clutter which can, in turn, blur real problem indications.
The task of finding faults in the network becomes strenuous because of the volume of static and transient indications masking potential serious real problem indications. One problem can give rise to a mass of error indications. For example, a break in a fibre carrying many signals may be indicated at the end of the fibre but components further away carrying aggregate signals or components of these signals may also indicate the fault and entities even further away do likewise. If a bundle of fibres are broken, for example by a digger, the network may give rise to thousands or even tens of thousands of error indications. These indications have a tendency almost to occur almost simultaneously, thereby swamping the system.
The network may also suffer small problems that can occur at the same time as the system is already swamped with the plethora of indications arising from a fault as previously mentioned. It can also be the case that a local fibre break can prevent problem indications being propagated with the result that distant problem indication indications are received first. This can make it almost impossible to locate the smaller local problems. It is of course possible that the smaller local problem may have more serious consequences to traffic and to the integrity of the network than the distant problems swamping the problem indication systems. Added to this, there are the possibilities that detectors themselves may be operating incorrectly and there may be intermittent faults in the problem indication system itself. A small fault may have intermittencies that can cause masses of changes in the problem indication. As a result of these difficulties, some networks use human operators literally sitting in front of monitors watching streams of error indications. Other systems employ a rule-based monitoring set up such that a break in one location triggers a series of reactions according to a set of rules so as to generate an error indication in a deterministic sense.